1. Field of the Invention
The present invention relates to a fuel cell, and more particularly, to a fuel cell having means for sealing a manifold for the intake and exhaust of a fuel gas and an oxidant gas.
2. Description of the Related Art
A fuel cell, e.g., a molten carbonate fuel cell, comprises unit cells which are each formed of a porous anode, a porous cathode, and an electrolyte tile interposed between them. When a fuel gas and an oxidant gas are supplied to the anode and the cathode, respectively, in each unit cell, an electrode reaction is caused, so that electric energy is produced. Voltage produced by each unit cell is as low as 1 V. Therefore, a number of unit cells are stacked in layers, and a number of conductive separator elements are interposed between the unit cells to connect them electrically, thus constituting a stacked structure. Thus, the fuel cell can produce high voltage.
The two gasses must be prevented from leaking out of the stacked structure and from mixing with each other, and the adjacent separator elements must be electrically insulated from one another. Therefore, the peripheral regions of separator elements and those of the electrolyte tiles are stacked in contact with each other, and then are sealed by a wet-seal system. More specifically, the temperature of the stacked structure is raised to 650.degree. C. or the working temperature of the fuel cell. When the temperature of the material of the electrolyte tiles attains 488.degree. C., in the course of the temperature rise, the electrolyte material melts. The molten substance fills up the gaps between the contact surfaces of the separator elements and the electrolyte tiles. Thus, the stacked structure is sealed and the adjacent separators are insulated from one another.
Formed inside the stacked structure are fuel gas manifolds for the intake and exhaust of the fuel cell into and from the anodes of the individual unit cells, and oxidant gas manifolds for the intake and exhaust of the oxidant gas into and from the cathodes of the unit cells. In each manifold, through holes or segment channels bored through the peripheral regions of the separator elements communicate individually with through holes or segment channels bored through the peripheral regions of the electrolyte tiles. Since the peripheral regions of the separators and those of the electrolyte tiles are sealed by the wet-seal system, the gases are prevented from leaking out through the boundaries between the through holes of the separator elements and the electrolyte tiles, that is, the manifolds are sealed.
However, there is a possibility of the performance of the aforementioned seal being unsatisfactory, due to the wettability of the electrolyte tiles, variation of the thickness accuracy of the separator elements and the elements constituting the unit cells, variation of applied pressure, variation of the accuracy of the contact surfaces of the separator elements and the electrolyte tiles, etc. In consequence, the fuel gas and the oxidant gas may possibly leak out and be mixed with each other, so that they cannot be effectively used.